A network engineer is configuring AAA on a Cisco ISR router to authenticate administrative users via a RADIUS server. The engineer configures the router with the command 'aaa new-model' and then 'aaa authentication login default group radius local'. When the engineer attempts to SSH to the router using a username that exists only on the RADIUS server, the authentication fails. The RADIUS server is reachable and the shared secret is correct. What is the most likely cause of the failure?

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